One of the most revolutionary technologies of the Internet age has been the search engine. Internet users instantly have access to a wealth of information by typing a few words (e.g., keywords) relevant to the thing they are interested in. The success of the text-based search engine at providing a user with information in response to a text query, and the proliferation of mobile cameras, have created a demand for visual search, where a user provides an image and is seeking information in response. Here the user may not know the words to describe his image, or may find text entry inconvenient or impossible, and thus traditional text search is not useful to him. He may desire to know what the image is of or to find information about an object in the image, or where to get something like an object in the image (e.g., procure or purchase the object in the image), or what the name of a person in the image is, or he may want some information extracted from the image (e.g., the time on a clock, the code from a barcode, etc.). Image search has lagged text search because of the difficulties of computer vision processing. Recognizing images within a strict framework (e.g., reading the time off of a clock) is relatively easy, however, recognizing any object without restriction can be quite difficult.